1. Field of the Invention
The present invention relates to a liquid recorder apparatus and method utilizing multiple power pulses to eject liquid from multiple emitters. In particular, the present invention relates to an apparatus and method for interleaving in time the power pulses directed to the emitters.
2. Description of Related Art
A thermal ink jet printhead selectively ejects droplets of ink from a plurality of drop emitters to create a desired image on an image receiving member, such as a sheet of paper. The printhead typically comprises an array of the drop emitters that convey ink to the image receiving member. In a carriage-type ink jet printhead, the printhead moves back and forth relative to the image receiving member to print the image in swaths. Alternatively, the array may extend across the entire width of the image receiving member to form a full-width printhead. Full-width printheads remain stationary as the image receiving member moves in a direction substantially perpendicular to the array of drop emitters.
An ink jet printhead typically comprises a plurality of ink passageways, such as capillary channels. Each channel has a nozzle and is connected to an ink supply manifold. Ink from the manifold is retained within each channel until, in response to an appropriate signal applied to a resistive heating element in each channel, the ink and a portion of the channel adjacent to the heating element is rapidly heated and vaporized. Rapid vaporization of some of the ink in the channel creates a bubble that causes a quantity of ink (an ink droplet or a main ink droplet and smaller satellite drops) to be ejected from the emitter to the image receiving member. U.S. Pat. No. 4,774,530 to Hawkins, the disclosure of which is incorporated herein by reference, shows a general configuration of a typical ink jet printhead.
U.S. Pat. No. 4,982,119 to Dunn, the disclosure of which is incorporated herein by reference, discloses a method and apparatus for gray scale printing with a thermal ink jet pen. A firing resistor is driven by a plurality of pulses to eject a droplet of ink from a nozzle. Prewarming of the ink in the firing chamber is achieved by applying an electrical warming pulse signal to the resistor prior to a firing pulse signal. The firing pulse signal causes the drop to be ejected. The warming pulse may be a plurality of pulses applied sequentially prior to the firing pulse and transfers a desired quantity of thermal energy to the ink. The prewarming of the ink by the warming pulse or pulses increases the volume of the ink droplet. By varying the degree of prewarming, the droplets ejected by the firing pulse can be varied in volume, yielding gray scale printing.
European Patent Application No. 0 496 525 A1, the disclosure of which is incorporated herein by reference, discloses an ink jet recording method and apparatus in which ink is ejected by thermal energy produced by a heat generating element of a recording head. According to one aspect, driving means apply plural driving signals to the heat generating element for every ink droplet ejected. The plural driving signals include a first driving signal for increasing a temperature of the ink adjacent the heater without creating the bubble, and a second driving signal subsequent to the first driving signal with an interval therebetween, for ejecting the ink. Additionally, a width of the first driving signal is adjustable so as to change an amount of the ejected ink.
European Patent Application No. 0 505 154 A2, the disclosure of which is incorporated herein by reference, discloses a thermal ink jet recording method and apparatus which controls an ink ejection quantity by changing driving signals supplied to the recording head on the basis of a variation in temperature of the recording head. A preheat pulse is applied to the ink for controlling ink temperature and is set to a value which does not cause a bubble forming phenomenon in the ink. After a predetermined time interval, a main heat pulse is applied which forms a bubble in the ink to cause ejection of a droplet (or a main droplet and satellite drops) of ink from an ejection port.
All of the above patents use multiple pulses applied to a heater element to eject a single drop of ink from an ejector (emitter). One or more pulses are used as a prewarming (or precursor) pulse to warm the ink while a subsequent drive pulse is used to eject a drop of ink from an ejector. In such conventional ink jet printers, the precursor and drive pulses are provided sequentially to each of the heater elements or to banks of heater elements. That is, the precursor pulses and driving pulse are applied to a first heater element or bank of heater elements, followed by application of precursor and drive pulses to a second heater element or bank of heater elements, and so on. Accordingly, the time necessary to drive an entire printhead of such heater elements will be at least the sum of the durations of all the precursor and drive pulses applied to each of the heater elements or banks of heater elements, plus any relaxation time between the pulses.
In such conventional ink jet printers, the precursor pulses are applied to all of the heater elements of the array whether or not a subsequent drive pulse will be applied to actually eject a drop from each emitter. This procedure uses unnecessary electrical power, warming the printhead even when the data contains few image pixels, such as when printing text and line graphics.
U.S. patent application Ser. No. 08/220,720 to Stephany, the disclosure of which is incorporated herein by reference, discloses a power control system for a printer which has at least one heating element for producing spots. The system includes a thermistor disposed on a printhead which senses the temperature of the printhead. The sensed temperature is used to vary pulses applied to the at least one heating element to maintain a constant spot size.
Accordingly, there is a need to provide a method and apparatus that will enable printing using precursor and drive pulses in a more energy and time efficient manner, allowing faster printing and reduction in waste heat generation.